Create new detection rule set documentation to be included in the new docs. (#4508)

* move docs folder to docs-dev

* Add new docs folder

* update docset.yml to reflect latest usage

* Add rules_building_block folder

* revert changes to docs-dev/experimental-machine-learning/url-spoof.md

* bump patch versions

* revert bump

---------

Co-authored-by: Mika Ayenson, PhD <Mikaayenson@users.noreply.github.com>
Co-authored-by: Terrance DeJesus <99630311+terrancedejesus@users.noreply.github.com>

docs/docset.yml

@@ -0,0 +1,16 @@
+project: 'detection rules'
+cross_links:
+  - docs-content
+exclude:
+  - '_*.md'
+  - 'README.md'
+subs:
+  stack: Elastic Stack
+
+extensions:
+  - detection-rules
+  
+toc:
+  - file: index.md
+    detection_rules: ['../rules', '../rules_building_block']
+

docs/index.md

@@ -0,0 +1,3 @@
+# Detection rules
+
+Landing / overview page